Electrical amplifying devices



Aug. 21, 1956 G. M. CLARKE ELECTRICAL AMPLIFYING DEVICES Filed July 24, 1951 2 Sheets-Sheet 1 fan HAN] Value-Y GAR"! ATTORNEY G. M. CLARKE ELECTRICAL AMPLIFYING DEVICES Aug. 21, 1956 2 Sheets-Sheet 2 Filed July 24, 1951 INvE R G'RAHAM MORLEY a '3! z: i g'r' 'o RNEY United States atcntfiflice Patented Aug. 21,1956

ELECTRICAL AMPLEYING DEVICES Morley Clarke, Hounslovv, England, assignor to TheM-'1Valve Company Limited, London, England -Thisinvention relates to electric amplifying devices of the kindtin which an-electromagnetic wave to be amplified is-caused'to interact with, so as to extract energy from, electrons moving between two conductors under the infiu ence of an" electrostatic field applied between the conductors.

In'such'devices the electrons are caused to flow as a stream along the space between the two conductors under the influence ofa magnetic field transverse to the electro-' static field, and the electromagnetic wave is arranged to flow between theconductors, which act as a guide therefor,at eif'e'ctively'the same velocity as the stream, so that by interaction. with the electrons energy is progressively gained by the wave; the interaction results initially in..a transfer of energy both to and from the field, but electrons'whic'h'gain energyfrom the field are quickly returne'dto one of the conductors and take no furtherpart inth'e interaction, whilst the electrons which lose energy become focussed in bunches which move with'the electromagnetic wave so' as to transfer energy progressively thereto untilthese electrons are collected by the other of the two conductors.

The streamoffelectrons may be provided 'by a single electron. emissive cathode within the space between the twoconductors, either localised to a. small region of the space orlextending along the whole of it along the surface of one of (the conductors, or a plurality of separately spaced thermionic cathodes may be used.

In'order toreduce. the velocity of propagation of the electromagnetic wave to that of the electron stream, it is"'necessary to introduce wave-retarding means in the space between the conductors, and this means has hitherto usually consisted'of separate fins extending from one or both of the conductors partly across the said space.

. Su'chfins, however, introduce difficulties in the way of multiple resonances and, moreover, with the known arrangements, it is not easyto provide a satisfactory matchirigfbetween the arrangement comprising the two conductors and ieithcr the input arrangement from whichthe electromagnetic waveto be amplified is fed "to the conductors, or-the output arrangement by means of which the amplified wave is extracted from the conductors.

The object of this invention is to provide a novel form of device of the kind referred to in which these difficulties are reduced.

According to. the invention an amplifying device of the kind referred to comprises two coaxial conductors at least one of which. supports one or more helical partitions which each extendtowards the other conductor acrosspart of the. space between the conductors so as in effect to form a slotted'waveguide woundin a helix round the inner conductor, the partition or'partitions providingopposite sidewalls of .this waveguide and slots elfectively being formed .in. each of these side walls by the gaps either between opposing partitions extendingfrom different con.- ductors or between oneconductor and apartition or par.- titionseextending fromt the other. conductor, means are 2' provided for producing a circular, magnetic field" inr,the space between and concentric with said conductors; one or more electron emissive cathodes 'isorareprovide'd adjacent to1,the space traversingthe aligned' slots in sue,- cessive turns of the wave guide, and the said waveguide is continued away from the conductors at, each end'by a length of waveguide of which'thelength atone end constitutes or forms part of the input arrangement for feeding the electromagnetic wave to, be amplifiedintoith'e device, and the length at the other end constitutes orforrns partof the output arrangement for. extracting the amplified wave from the device after transmission through said helical slotted waveguide.

The partitions may either provide a spacedturn wave: guide, that is, to say of the kind formed by coiling a wave guide into a helix with adjacent turns, spaced apart, or a contiguous turn waveguide, that is to say one in which a single wall separates adjacent turns, asina screwathread.

Preferably each of thesaid one or more partit'ons .ex; tends approximately perpendicular to thecommonaxis' the conductors so that the partitons and conductors to; gether form a slotted Waveguide ofsubstantially rectangu; lar cross-section, and preferably the partitions extend from only oneof the conductors, the otherconductor carrying on its surface one or more electron emissive cathodes; in some cases a single cathodemay extenduover substan; tially the whole of the surface, of said conducton,

Preferably themeans for producing the circular mag; netic fieldbetween the concentric conductors consists. ,of means for passingan electric current alongthe inner con; ductfor, which current may in some cases. serve.. at.f the same time as a heatingcurrentforan. electron-emissive cathodeor cathodes provided at, the surface of.the,inner conductor. A circular, magnetic field is, of course,; re? quired with. concentric conductors to produce. axialflow of the electrons under the influence of the magnetic field and the radial. electrostaticfield applied betweenthe ,conductors. In some cases the electrostatic field,,rnay be applied in pulses, and the. current establishing themagnefic field may then also'bepulsed in synchronism therewith; when thecurrent serves alsoforheating a cathode, the efiective heating of the. cathode may becontrolled by varying the. duration. of thecurrent pulses.

In the operation of an amplifying device. in accordance with the.;invention, the electromagnetic. wave is trans; mitted round. the helicalv slotted=waveguide,, formed ,by theone .or. more partitions and the conductors,.in agmode havinga component of electric intensity directedvalong the axis of. theconduct'ors, and the magnetic andyeleotr-o,- static, fields are arranged to produce in thespaces1ravers-, ing, the aligned slots of the waveguide,which-willhereiu: after-be referred to as the reaction space, a-flow of;; elec trons along said axis atsa velocity which isxsubstantially equal to therefiective velocity ofi phase ,propagatipn of the electriofield axially along ,said reaction space;

The. effective retardation of the electromagneticswave is thus effected by virtue of-the longerzpath, for a given axial length of the conductors, which thewave is caused to travel round the helical waveguideformed by the one or more partitions and the conductorsgthe electrons-react With the fringing electric fields formed across the aligned slots in successive turns of the waveguide.-

Preferably the helical wave-guide is ,of substantially rectangular cross-section: and the electromagneticnwave is arranged tobe fed to it along, the input waveguide-in-the H10 mode, with electric fielddirected along the, axis of said conductors.

By: continuing the helical Waveguideat each-end. toform input and output Waveguides, the. difiiculties ofnnatching are largely overome. i

The amplifying device, in accordance ;with the-invention is, of course, intended to operate with an evacuated reaction space, and the outer conductor and input and output waveguides, suitably sealed, may conveniently form part of the evacuated envelope. 7

The invention will be further explained with reference to the accompanying schematic drawings in which Figure 1 shows a perspective view of one embodiment of the invention with partly cut-away outer wall, Figure 2 represents a fragmentary section along the axis of the embodiment of Figure l, and Figure 3 shows in perspective a second embodiment of the invention with partly cut away outer wall.

Referring now to Figures 1 and 2, the amplifying device shown comprises an inner conductor in the form of cylindrical metal tube 1 which is insulatingly supported along the axis of a cylindrical outer metal tube 2 at each end by a glass annulus 3 sealed on one side to a flange 4 projecting radially outwards from the inner conductor and on the other side to a flange 5 projecting radially inwards from the outer conductor.

The outer conductor 2 supports a single helical partition 6 which extends towards the inner conductor 1 but does not touch it, leaving gaps 7 which define by their alignment an approximately cylindrical reaction space surrounding the inner conductor. The inner conductor is coated on its outer surface, that is to say the surface facing the partition 6, for most of its length with electron emissive material 8, for example alkaline earth oxide (see Figure 2), and an electric resistance heating element 14 is contained within the inner conductor ll.

7 At each end the rectangular-section waveguide constituted by the adjacent turns of the partition 6 and by the conductors l, 2 is continued by short lengths 9, lib of similar section waveguide each soldered into an aperture in the outer conductor and each hermetically closed by a glass window 11, 12 respectively, sealed therein.

The device is provided with a glass or metal side stem 13 by which it is evacuated and sealed off during manufacture, a metal stern closed by a cold-weld cut-off being shown.

In operation of the device the input wave to be amplified is fed into the waveguide 9, say, in the H mode with the electric field directed parallel to the axis of the conductors. The outer conductor 2 is maintained at a suitable positive potential relative to the conductor 1, and a unidirectional current is passed along the inner conductor .1, the potential at 9 being negative relative to the potential at'lti, so that the electrostatic and magnetic fields thereby produced together give rise to a progression of electrons emitted from the coating 8 on the surface of the inner conductor 1 in the direction from 9 to It The inner conductor 1 is raised to the temperature required for the emission of electrons from the coating 8 both by the unidirectional current passed through the conductor and by the passage of a suitable heating current through the heater 14.

Referring now to the fragmentary axial section shown in Figure 2, the arrowed dotted lines indicate at one instant the nature and direction of the electric fringing fields formed at the gaps 7 by the input wave. It will be apparent that an electron at A travelling in the direction rom 9 to 10 will give up energy to the facing electric field as it progresses from A to B, and the velocity of progression is arranged by control of the magnitude of the direct current flowing along 1 and the voltage between 1 and 2, to be such that by the time the electron has reached B the facing electric field has oscillated to a retarding phase. In this way a repeated transfer of energy from the electrons to the electromagnetic field is obtained and an amplified output wave is taken from the waveguide iii.

The amplifying device shown in Figure 3 is in effect the inverse of that shown in Figures 1 and 2. An inner conductor is supported axially within an outer conductor 16, by flanges 17, 18 and a glass annulus 19 at each and similar to those described with reference to Figure l. The inner conductor 15 carries a helical waveguide-forming petition 20 leaving a gap 21 which forms the electron reaction space. The inner surface of the outer conductor is coated with electron emissive material 22 and a heating coil 23 is wound round the outer conductor for raising the material to its electron emissive temperature in operation; the coil 23 is wound in coiled coil form for minimising the magnetic field produced by it within the space between the conductors.

The waveguide formed by the partition 20 is eflfectively continued at each end by short lengths 24, 25 of similar section waveguide soldered into apertures in the outer conductor 16 and sealed by means of glass Windows 26, 27 respectively.

The device is evacuated and sealed off during manufacture by means of a side-stem 28 shown as a metal tube closed by a cold-Weld cut-off.

The operation of this device is similar to that described with reference to Figure 1 except that in this case the inner conductor 15 is maintained at a positive potential relative to the outer conductor 16 and the direction of the direct current passed through the inner conductor for generating the magnetic field is reversed for operation with 24 as the input end and 25 the output end.

The partition 20 and inner conductor 15 may conveniently be formed in one piece by cutting a deep helical groove, the wall of which forms the partition, in a solid rod.

What we claim is:

1. An amplifying device for amplifying an electromagnetic wave by interaction with a moving stream of electrons, comprising within an evacuated space a pair of mutually insulated coaxial conductors, at least one helical partition supported in the annular space between said conductors and extending part way across this space to form a slotted waveguide wound in a helix round the inner conductor, means for producing :a circular magnetic field concentric with said conductors in said annular space between them, at least one electron emissive cathode arranged in said annular space for producing a stream of electrons through the part of the space traversing the aligned slots in successive turns of the helical waveguide under the influence of the circular magnetic field and a radial electrostatic field applied between said coaxial conductors, input means for feeding into one end of said helical waveguide the electromagnetic wave to'be amplified and output means for extracting from the other end of said waveguide the wave amplified during its passage through the waveguide by interaction with said stream of electrons.

2. An amplifying device according to claim 1 wherein the input means and output means each consists of a length of waveguide coupled to said' coaxial conductors at each end thereof so as to form a continuation of said slotted helical waveguide.

3. An amplifying device according to claim 1 wherein the partition extends perpendicular to the common axis of said coaxial conductors so that the slotted helical waveguide is formed with substantially rectangular crosssection.

4. An amplifying device according to claim 1 wherein an evacuated envelope is provided of which the oo-axial conductors form part.

5. An amplifying device according to claim 1 wherein the input means and output means each consists of a length of waveguide branched from the end of said coaxial conductors so as to form a continuation of said slotted helical waveguide, wherein the device includes an evacuated envelope of which the input and output waveguides form part and wherein wave-transmissive windows seal the input and output waveguides.

6. An amplifying device according to claim 1 wherein a single helical partition extends from only one of the coaxial conductors, and the electron emissive cathode is formed on the surface of the other of said conductors. 7. An amplifying device according to claim 6 wherein the cathode extends over substantially the whole of the surface of the other conductor.

8. An amplifying device according to claim 1 wherein the means for producing a circular magnetic field 0onsists of means for passing an electric current along the 5 inner conductor.

References Cited in the file of this patent UNITED STATES PATENTS 2,122,538 Potter July 5, 1938 10 

